The proposed studies will examine phosphodiesterase (PDE) activity and calmodulin (CaM) in relation to cyclic nucleotide metabolism in developing salivary glands and their relationship to development of the stimulus-secretion response system. It has already been established that in the rat submandibular gland (SMG), the stimulus-secretion response system does not become operational until 5-6 days postnatal, coincident with the appearance of B-adrenergic receptors. Adenylate cyclase (AC) activity in rat SMG is present at an early embryonic age, reaches maximal levels by 18 days in utero, and remains at that level through adulthood. Since AC activity remains constant through the period of the development of a functional stimulus-response system, it is our hypothesis that in order to accommodate the change in cyclic nucleotide regulation that accompanies the postnatal development of the stimulus-secretion coupling mechanism, parallel changes will occur in the PDE enzymes in the developing gland. This proposal will therefore examine the developmental regulation of PDE and its endogenous regulator, CaM, in the developing rat SMG. Steady state levels of cAMP will also be measured. Studies will concentrate on changes in the pattern and regulation of isozymic forms of PDE, including changes in the activity, physical properties, kinetics, substrate specificity, and subcellular localization of the PDE isozymes and their regulation by CaM. Changes in CaM content and its subcellular localization will also be examined. The analysis of the subcellular localization of PDE isozymes will be conducted through a concerted approach using biochemical, histocytochemical and immunocytochemical means, employing monoclonal antibodies directed against different PDE isozymes and CaM. Following extensive analysis of the developing SMG, time permitting, studies will be extended for confirmation to developing parotid and sublingual glands. The results of these studies will shed light on the manner in which cAMP metabolism is regulated in relation to the evolution of the stimulus-secretion coupling mechanism. Further, this study will provide, for the first time, a picture of the subcellular localization of specific PDE isozymes which can serve as a general model for other systems.